Modelling Antarctic and Greenland volume changes during the 20th and 21st centuries forced by GCM time slice integrations

Current and future volume changes of the Greenland and Antarctic ice sheets depend on modem mass balance changes and on the ice-dynamic response to the environmental forcing on time scales as far back as the last glacial period. Here we focus on model predictions for the 20th and 21st centuries using 3-D thermomechanical ice sheet/ice shelf models driven by climate scenarios obtained from General Circulation Models. High-resolution anomaly patterns from the ECHAM4 and HadAM3H time slice integrations are scaled with time series from a variety of lower-resolution Atmosphere-Ocean General Circulation Models (AOGCM) to obtain the spread of results for the same emission scenario and the same set of ice-sheet model parameters. Particular attention is paid to the technique of pattern scaling and on how GCM based predictions differ from older ice-sheet model results based on more parameterised mass-balance treatments. As a general result, it is found that the effect of increased precipitation on Antarctica dominates over the effect of increased melting on Greenland for the entire range of predictions, so that both polar ice sheets combined would gain mass in the 21st century. The results are very similar for both time-slice patterns driven by the underlying time evolution series with most of the scatter in the results caused by the variability in the lower-resolution AOGCMs. Combining these results with the long-term background trend yields a 20th and 21st century sea-level trend from polar ice sheets that is however not significantly different from zero. (C) 2004 Elsevier B.V All rights reserved.